While vaned diffusers can achieve superior performance relative to vaneless diffusers, this superior performance can, in general, only be achieved over a limited range of flow rates. In contrast, vaneless diffusers, while not capable of the superior performance of vaned diffusers, can maintain an acceptable performance over a broad range of flow rates. In order to achieve the high performance of a vaned diffuser over a broad range of flow rates, many systems have been suggested that enable the setting angle of the diffuser vanes to be varied continuously with flow rate. This allows acceptable diffuser incidence angles to be maintained over a broader range of flow rates. However, existing variable geometry systems are characterized by complicated linkages that rotate each diffuser vane by an appropriate amount in response to the varying flow rate. These systems are expensive and are prone to mechanical problems due to the multiplicity of moving parts needed to rotate all the vanes. Thus, a need exists for an inexpensive, simplified mechanism that can appropriately vary the setting angle of the vanes as the flow rate varies.
Diffuser vanes are normally designed with a constant geometry such that the entire height of the vane has the same setting angle. The exit flow profile from an impeller, however, is typically distorted and nonconstant depending on the design details of the impeller as well as overall parameters such as specific speed. Thus, a vane set to a particular stagger angle might match with part of the flow while mismatching with other parts of the flow. For example, if a diffuser vane is adjusted such that its angle of incidence matches the exit flow at the hub, most likely the angle of incidence of the vane will not match the exit flow at the shroud. This lack of incidence matching creates undesired inefficiencies. Thus, a need exists for a diffuser vane that provides improved angle of incidence matching between the vane leading edge and the exit flow from the impeller and maintains desired incidence angles as the flow rate is varied via the use of a simple variable geometry system.